The basic structure of a typical integrated circuit (IC) comprises a rectangular semiconductor die or chip surrounded by and connected to a number of fine wire leads which are further connected to a surrounding frame of thicker metallic traces which in turn form the external pins of the IC. With the exception of the external pins, the entire assembly is typically encapsulated in a package comprised of a mold compound. When an IC is installed on a circuit board, the pins of the IC are typically soldered to corresponding pads on the circuit board. A complex IC installed on a circuit board can fail for any of a large variety of reasons, including, among others, failures of the internal die or chip, failures of the many fine wire leads attached to the die and failures of the many connection joints between the die, the wire leads and the surrounding pin frame. Determining the cause of failure of even one of many mass-produced ICs can provide valuable information for preventing future failures and improving IC manufacturing processes.
In many cases, the only way to identify the cause of failure of an IC is by a visual inspection of the interior of the IC, namely, the die, the wire leads, the pin frame and the solder connections therebetween. Moreover, physical access to interior points may also be needed to isolate problems. For instance, physical access can allow an analyzer to electrically probe sections of the IC to determine functionality. While X-ray and ultrasonic imaging techniques can provide visual information, they do not afford physical or electrical access to internal points.
Removing the molding compound that surrounds the IC die, the associated wiring and/or the pin frame can provide both visual and physical access to the critical potential failure points. Doing so, however, in a way that does not introduce further damage has proven difficult if not impossible. Conventional methods have been known to damage the very fine leads or die, making determination of the true cause of failure impossible. Furthermore, it is often desirable when performing failure analysis, to power-up and operate the IC while in an exposed state. If removing the molding compound damages the IC rendering it inoperative, such analysis is not possible.
A method and system is therefore needed that can remove the mold compound of an IC to provide both physical and visual access to the delicate interior structure of the IC without damaging said interior structure.
Another potential source of IC failures relates to the molding compound itself. Often, due to impurities or inconsistencies in the composition of the molding compound, “hot spots” or areas of elevated temperature can occur in parts of the IC which can cause or contribute to the failure or degradation of a section or all of the IC. Preventing such hot spots is particularly critical for high-speed, complex ICs which often require auxiliary cooling measures such as fans and heat sinks in their normal operation. In order to avoid such defects in the molding compound of future devices, it would be desirable to analyze the composition of the molding compound of devices that have failed in order to determine if such defects were present, the nature of such defects and the location of such defects. There are no known satisfactory methods or systems for doing so.
Another issue related to the failure analysis of electrical circuitry that has not been adequately addressed in the prior art entails the accurate cutting of the circuit board on which a failed device is installed. When performing failure analysis on a component such as an IC that is installed on a circuit board, it is often necessary or desirable to remove the component from the circuit board. Known methods include cutting the circuit board around the component using such tools as a fine diamond saw or a water jet. The widths of the cuts formed with such machines are typically 0.005″-0.030″. Moreover, such mechanical methods of cutting introduce substantial vibration which may harm surrounding components or their connections to the circuit board. The potential damage to the area or components adjacent to a cut is also a concern in production processes such as singulation, in which one or more smaller circuit boards are separated from a larger board. To maximize circuit board density, it is often necessary to place components close to the edges of the boards. Conventional cutting processes, which have large cutting widths and which can cause damage to features near the cut, limit the ability to place components close to the board edges.
Because of the ever increasing density of components installed on a circuit board, a need therefore exists for a method of cutting a circuit board which provides a very fine cut and also minimizes any damage to the area surrounding the cut.